A load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred. To improve efficiency, a power factor correction (PFC) circuit dynamically adjusts the current drawn from an alternating current (AC) power source so the current substantially follows the voltage of the power source. For example, more current is drawn when the voltage of the power source is higher. In general, a PFC circuit actively pulses incoming current in accordance with the shape of the incoming voltage, and provides a substantially constant current output. A PFC circuit is often used in conjunction with switching power supplies.